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TitleGeochemistry and petrogenesis of the Black Thor intrusive complex and associated chromite mineralization, McFaulds Lake greenstone belt, Ontario
LicencePlease note the adoption of the Open Government Licence - Canada supersedes any previous licences.
AuthorCarson, H J E; Lesher, C M; Houlé, M G
SourceTargeted Geoscience Initiative 4: Canadian nickel-copper-platinum group elements-chromium ore systems -- fertility, pathfinders, new and revised models; by Ames, D EORCID logo (ed.); Houlé, M G (ed.); Geological Survey of Canada, Open File 7856, 2015 p. 87-102, Open Access logo Open Access
PublisherNatural Resources Canada
Documentopen file
Mediaon-line; digital
RelatedThis publication is contained in Targeted Geoscience Initiative 4: Canadian nickel-copper-platinum group elements-chromium ore systems -- fertility, pathfinders, new and revised models
File formatpdf
Lat/Long WENS -86.2278 -86.1783 52.7969 52.7722
Subjectsmetallic minerals; igneous and metamorphic petrology; petrogenesis; nickel; platinum; chromium; ore mineral genesis; metallogeny; chromite; mineralization; modelling; trace element geochemistry; whole rock geochemistry; stratigraphic analyses; Black Thor intrusive complex; Superior Province; Precambrian
ProgramTargeted Geoscience Initiative (TGI-4) Mafic-Ultramafic Ore Systems
Released2015 06 22; 2023 03 17
AbstractThe Black Thor intrusive complex (BTIC) contains a conduit-hosted, stratiform Cr-Ni-Cu-(PGE) deposit with a very large amount of chromite for an intrusion of its size. Most conduit-hosted stratiform deposits are Archean, formed from komatiitic magmas containing approximately 3000 ppm Cr2O3, and are typically saturated in chromite. The fundamental problem in understanding the genesis of the BTIC deposit and other deposits of this type is explaining how such large quantities of chromite crystalized from a magma that normally crystallizes only small amounts chromite and normally have a chromite:olivine abundance ratio of ~1:60. Current genetic models, such as in situ crystallization (by oxidation, pressure increase, magma mixing, and/or wholesale assimilation of felsic rocks or iron formation) or physical transportation of chromite slurries do not provide a wholly satisfactory explanation for the high abundance of chromite in this type of deposit. We are testing an alternative model: partial assimilation (as opposed to wholesale assimilation) of local oxide-silicate-facies iron formation by a Cr-rich magma. As low-Mg komatiite is saturated in chromite, the magma may dissolve the silicate component (quartz/chert and Fe-silicate minerals) of the iron formation, but would be unable to dissolve the oxide component (magnetite). Through interaction with the hightemperature (1400°C) Cr-rich magma, the fine-grained magnetite could be upgraded via diffusion to chromite during transportation within the conduit. This upgrading is similar to the upgrading of barren sulphide xenomelts that has been proposed for Ni-Cu-(PGE) deposits.
Summary(Plain Language Summary, not published)
The Targeted Geoscience Initiative (TGI-4) is a collaborative federal geoscience program that provides industry with the next generation of geoscience knowledge and innovative techniques to better detect buried mineral deposits, thereby reducing some of the risks of exploration. This volume summarizes 22 research activities completed under the TGI-4 Ni-Cu-PGE-Cr ore systems project that focused on revised and new geologic models for Ni-Cu-PGE, PGE-Cu and Cr deposits, innovative techniques for determining potential fertility of intrusion (Ni-Cu-PGE), and defining pathfinders for Ni-Cu-PGE mineralization.

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